Electrical method of mechanically connecting and mutually insulating spaced metal elements



April 15, 1947- LODWlG 2,419,149

ELECTRICAL METHOD OF MECHANICALLY CONNECTING AND MUTUALLY INSULATING SPACED METAL ELEMENTS Filed Jan. 1, 1944 2 Sheets-Sheet l L I L INYENT M& 7

ATTORNEYS April 15, 1947. E. LODWIG 2,419,149

ELECTRICAL METHOD OF MECHANICALLY CONNECTING AND MUTUALLY INSULATI Filed Jan. 1, 1944 N6 SPAGED METAL ELEMENTS 2 Sheets-Sheet 2 Iv M ATTORNEYS Patented Apr. 15, 1947 ELECTRICAL METHOD OF MECHANICALLY CONNECTING AND MUTUALLY INSULAT ING SPACER METAL ELEMENTS Erwin Ludwig,

Mobile Refrigeration, Inc, Long Island Franklin Square, N. Y., assignor to City,

N. 11., a corporation of New York Application January 1, 1944, Serial No. 516,731 2 Claims. ((31. 219-) This invention relates to a method of making insulated structures and more particularly an improved structure incorporating spaced substan' electrical condensers are also formed of spaced 4 parallel conducting plates with the air therebetween acting as the dielectric. In these and like structures, it is essential that the adjacent conductive sheets be mechanically connected by suitable means at many points in order to strengthen the structure, to prevent vibration or Contact or the plates and for other reasons. It is, however, essential that the connections used be non-conducting so that the plates remain thermally or electrically isolated or both. In all structures of the type described and particularly those com prising relatively closely spaced sheets of considerable area, it is diflicult if not impossible by previously known means and methods to permanently secure insulating mechanical connectors between the substantially inaccessible portions of the sheets remote from their edges. This difficulty is aggravated when such connectors are to be simultaneously secured between three or four spaced parallel sheets.

With the above and other considerations in mind, it is proposed in accordance with the present invention to provide a multiple conductive sheet structure of the type described. in which the adjacent sheets are permanently mechanically connected in spaced substantially parallel re lation by insulating supports or connectors. A particular object of the invention is the provision of an improved method of permanently mechanically connecting metallic plates or sheets in spaced relation while maintaining them electrically and thermally isolated. Various other objects, advantages and characteristic features of the invention will be apparent from the following description.

' In describing the invention in detail. reference will be made to the accompanying drawing which illustrates certain embodiments thereof. in the drawings:

Fig. 1 is a simplified and diagrammatic elevation, taken edgewise of the plates, and showing a connector embodying the invention in position tobe welded between two metallic plates in accordance with the invention;

Fig. 2 is an elevation similar to Fig. '1 show- 2 ing the connector and plates after the weldin operation is completed;

Fig. 3 is an elevation of an insulating conhector of the type shown in Figs. 1 and 2;

Fig. 4 is a side elevation of one of a plurality of sheets interconnected in accordance with the invention;

Fig. 5 is an edge view of three sheets connected in accordance with the invention;

Figs. 6 and 7 are respectively sectional elevations of two modified forms of my improved insulating connector; and,

Figs. 8, 9 and 1c are respectively elevations i1- lustrating three different types of current sepa- 1rable links used in connection with connectors embodying the invention.

In general, the objects of the invention are carried out by means including a connector formed of material that is relatively non-concductive of heat or electricity or both and which has secured thereto oppositely disposed end pieces or caps of weldable conductive metal. The metal caps are electrically connected by a conductive link which is capable of carrying a heavy elec tric current of such magnitude and for a sufficient time interval to Weld the caps to metal plates or other parts but which is fusible or otherwise separable in response to the flow of such current for a longer time interval, or in response to a heavier current. Conductive links of this nature will be hereinafter referred to generically as current separable links, this term embracing both links of the nature of conventional slow blowing fuse links that are fusible by heat generated by the passage of current therethrough and links of the type employed in thermal overload cutouts that are separable by heat generated by the flow of current through an element other than the link itself.

The connector C shown in Figs. 1, 2 and 3 has a body 2 formed of molded thermal and electrical insulating material. This material may comprise a thermoplastic or thermosetting resin including the known resinous materials such as phenol formaldehyde and urea formaldehyde resins, hard rubber, or insulating compounds of the nature of hard rubber such as are available on the market and. known in the electrical art. End caps 12 or iron, steel or other weldable metal are permanently secured to the opposite ends of the insulating body it in any suitable manner as by inwardly crimping the edges l3 of the cap flanges i so that they are imbedded in the material forming the body 3 l. The end faces of the caps may be provided with one or more raised points or lugs l 5 which provide contact points of limited area for spot welding, although the provision or these points is not essential to the invention.

In order to form a circuit for the flow of weldlllg current; a current separable link I6 is connested between the two end caps l2. In the em bc-diment shown in Figs. 1, 2 and 3, the link I5 is a slow blowing fusible link of a type well known in the art. The opposite ends of the link l6 are suitably permanently secured to the flanges l4 of the respective caps l2 by means such as brazing, soldering, welding or the like. and the lini: is preferably disposed in spaced relation to the body I l of the connector. as shown in Fig. 1. The link l2 may be formed of a suitable known fuse metal such as lead or lead alloys, zinc or zinc alloys, Mont-1 metal, copper or aluminum. Its minimum cross section is such that it will melt and blow or open after currents suflicient to weld the end caps [2 to adjacent metal elements has flowed therethrough for a time interval somewhat greater than that required to form such welds. Known slow blowing fuse links of appropriate current capacity are suitable for this purpose. In general, such links are formed of fusible metal of considerable mass so that an appreciable time interval is required for current flow therethrough to heat the link to a melting temperature. In accordance with the known practice, the link 16 may be provided with spaced reduced sections as shown in Fig. 3 which insure a positive wide separation of the fused ends thereof.

My improved method of mechanically connect ing while thermally and electrically isolating eaced parallel plates or sheets of conducting material will now be described. As shown in Fig. l, a connector C of the type described is placed between the two adjacent plates P1 and P2. These plates may be closely spaced substantially parallel thin steel plates of the type having surfaces or surface coatings that reflect a high percentage of the heat rays incident thereon. The invention is of course not limited to the use or this material but embraces the connection of any weldable conductive plates including various structural panels and the plates of electrical condensers.

Two welding electrodes l8 and i9 are brought in contact with the outer surfaces of the plates Pl and P: respectively at points aligned with the ends of the connector C as shown. The structure comprising the plates and the interposed connector is preferably compre rely gripped between the electrodes 88 and la. This has been illustrated by the compressed spring 2!! interposed between a fixed support 21 and the electrode is, and insulated from the electrode by the block 2?! of insulating material. The other electrode l3 may be held by any suitable fixed insulated sup port 23. Obviously, other means may be used to clamp the structure set-ween the electrodes.

With the electrodes thus disposed. a welding current is caused to flow between them. Such current may be supplied in accordance with known practice from the secondary winding 2: of a welding transformer T, the winding being connected to the electrodes I 8 and ill by heavy low resistance cables 25 and 25. The secondary winding 24 may comprise one or two turns of heavy low resistance wire or cable. The primary winding 2' of the transformer T is energized from a suitable source of alternating current indicated at 28 through a switch 29. If necessary or de sirable, a series resistor 30 may be included in the supply circuit of the primary winding 21 and a push button switch 3! may be employed to shunt out the resistor 38 when it is desired to momen tarily increase the current output of the transformer T for a purpose to be described.

Closure of the switch 29 causes heavy current flow through the welding circuit including the secondary winding 24, the cables 25 and 26, the electrodes l8 and !9, the plates P1 and P2, the lugs E5, the caps l2 and the link I6. The points of highest resistance in this circuit are those at which the caps l2 contact the plates P1 and P2, and the temperature at the contacting surfaces quickly rises to a point where the metal of these parts softens and unites, this action being prometed by the pressure exerted by the electrodes on the composite structure. The time interval required to complete the welds is very short, particularly where the welds are of the nature of spot Welds due to the raised points or lugs [5 on the connector caps l2. Completion of the welds reduces the resistance of the welding circuit at the points of juncture between the caps l2 and the plates P1 and P2, and this ordinarily results in an increase in current after the welds are made. Immediately after the welds are made, the link l6 blows as shown in Fig. 2. The delay in blowing of the link until after the welds are made results from the above explained slow blowing characteristic of the link, and rapid blowing after completion of the weld may be caused or expedited by the automatic current increase noted above. If it is necessary or desirable to further expedite blowing of the link after the Welds are made, the push button shunt switch 31 may be momentarily closed to increase the current through the link.

The blowing of the link l5 thermally and eleotrically isolates the connector caps l2, and the disclosed operation thus both mechanically unites the plates and isolates them thermally and electrically. Where electrical insulation alone is desired, the body ll of the connector C may be formed of heat conductive insulating material such as porcelain, glass or the like.

The above described operation may be repeated as desired to secure any number of suitably spaced connectors C between the plates P1 and P2 as generally illustrated in Fig. 4. The operation may also be employed to simultaneously unite three spaced parallel plates or like members in which case one connector C is disposed between each adjacent pair of plates and the electrodes 58 and i9 are pro sed against the outer sur faces of the outer plates in alignment with the aligned connectors as illustrated in Fig. 5.

The weldable metal end pieces of my improved connector may be formed and secured to the insulating body portion thereof in various ways. As shown in Fig. 6, weldable metal end piece 35 having integral lockin extensions 36 on the inner faces thereof may be secured to the oppositely disposed surfaces of the insulating body H by molding the insulating material about the extensions 36 as shown. Acurrent separable link such as a fusible link it is connected between the end pieces 35 and fuses and opens in the manner described above after welds between the pieces 35 and adjacent metal elements are made.

The current separable link may be enclosed within the insulating body of the connector, and one such arrangement is illustrated in Fig. 7. As there shown, a central opening or bore 31 extends through the insulating body 33 between the locking extensions 36 of the two weldable meta-l end pieces 35. The current separable link, here shown as a fusible link 40, is secured at its ends to the locking extensions 36 and passes through the opening 37. A small lateral vent opening 39 may be provided to permit the escape from the passage 3'! of the gases generated when the link blows. The passage 31 may be centrally enlarged as shown so that any portions of the link 40 that may remain unconsumed after it blows cannot form a conductive path between end pieces 35.

In place of fusible links, I may employ other forms of current separable link or connections to electrically connect the weldable end pieces or caps of my improved connector during the welding operation. One such form is generally similar to the separable connections employed in overload thermal cutouts known in the art. The

. general arrangement includes a spring biased conductive link secured in current conducting connection between the end pieces by means including a metal or alloy that fuses or melts when heated to a predetermined temperature from some source other than the current passing therethrough, and when so fused or melted releases the spring biased link which then opens the connection.

One such alternative form of current separable link is illustrated in Fig. 8 where the connector C is of the same general structure as that disclosed in Figs. 1, 2 and 3 and described above. Here a link strip 4! formed of low resistance resilient metal such as high brass, spring steel or the like is welded or otherwise fixed at one end to one end ca 42 of the connector C and is bent in U-formation as shown so that its other end 43 is adjacent the opposite end cap 44. The material forming the link 41 is sufficiently resilient so that it will spring from the bent position shown in full lines to that shown in dotted lines in Fig. 8 unless its end 43 is fixed to the cap 44. A plate 45 of low resistance metal such as copper may be welded or otherwise fixed to the cap 44 to form a seat at which the link end 43 may be secured. The link end 43 is fixed to the plate 45 by a thin layer 46 of low resistance low melting point metal or alloy. When welding current passes between the plates P1 and P2, considerable heat is quickly generated at the end face of the cap 44 where the weld is formed, and this heat is conducted through the plate 45 to the metal quired to complete the weld. When sufficient heat has been thus conducted to raise the temperature of the layer 46 to its melting or fusing point, the end 43 is released and the strip 4l springs away from the cap 44 to approximately 4 the position shown in broken lines in Fig. 8, thus opening the electrical and thermal connection between the end caps 42 and 44.

As illustrated in Fig. 9, two spring strips and 48 may be end to one of the weldable end caps 49 and 59, and being spring biased to move to the open positions illustrated by broken lines. The strips 41 and 48 are connected by a layer of low resistance low melting point metal or alloy. When the welds between adjacent plates and the end caps 52 and 53 of the connector C are made, heat from the welds travels along the strips 41 and 48 to the fusible layer 5| and melts or fuses this layer, releasing the strips and so opening the link.

In the modification of Fig. 10, a heating unit in the form of a small grid or coil 54 of resistance wire is employed to furnish heat which melts the metal or alloy layer 55 that secures the free end of the outwardly biased spring strip 56 in the closed position shown. One end of the grid layer 46 during the time interval re employed, each being fixed at one ly low melting 54 is welded or otherwise fixed in electrical contact with the end cap 58 of the connector C and the other end thereof bears the layer which secures and electrically connects the free end of the Spring strip 56 in place. Upon the flow of welding current between the end caps 59 and 58, heat is generated in the grid 54 by the flow of this current therethrough, and after a time interval suiiicient to complete the welds between the caps and the adjacent plates or other metal parts, the heat so generated raises the temperature of the layer 55 to the melting or fusing point thereof and the strip 56 springs open. The heating grid or coil 54 may be readily modifled by changes in its dimensions or composition or both to provide a heating interval sufficient to permit completion of the welds before the link separates.

The metals or alloys employed to form the layers 46, 51 and 55 of the modifications disclosed in Figs. 8, 9 and 10 may comprise any metals or alloys of suflicient conductivity to carry the welding current without melting due to current flow through the layers themselves and of sufficientpoint to fuse and release the spring link or links at the temperature at which the layers are heated by heat from the weld or from the heating unit shortly after the welds are made. Suitable low fusing alloy of this nature are well known in the electrical art and are used for example in overload thermal cutouts.

I claim:

1. A method of mechanically connecting and mutually insulating a pair of spaced conductive metal elements which comprises interposing between the said elements a connector of electrical insulating material having spaced metal end pieces thereon respectively contacting said elements and a current separable link electrically connecting said end pieces, passing an electric current between said elements whereby said end pieces are respectively welded to said respective elements and passing additional current between said elements to open said current separable link after said end pieces are welded to said elements.

2. A method of mechanically connecting and mutually insulating a pair of spaced substantially parallel metal plates which comprises interposing between the adjacent surfaces of said plates a connector of electrical insulating material having spaced metal plate engaging end pieces electrically connected by a current separable link, passing electrical energy between the outer surfaces of said plates adjacent said connector whereby said end pieces are respectively welded to said adjacent plate surfaces by energy flowing through said link, and then passing additional energy between the outer surfaces of said plates to open said current separable link.

ERWIN LODWIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,111,749 Bussmann Mar. 22, 1938 1,278,911 Grifiith Sept. 17, 1918 2,140,709 Mauser 1. Dec. 20, 1938 

